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Evans-Tishchenko coupling of heteroaryl aldehydes
Philip D Dorgan1, Jamie Durrani, Manuel J Cases-Thomas
1School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, United Kingdom.
The Journal of Organic Chemistry
|October 9, 2010
Summary
Researchers developed a low-temperature Evans-Tishchenko coupling for heteroaryl aldehydes and β-hydroxy ketones. This method achieves high yields and diastereoselectivity, overcoming competing retro-aldol reactions at higher temperatures.
Area of Science:
- Organic Chemistry
- Catalysis
- Synthetic Methodology
Background:
- The Evans-Tishchenko reaction is a valuable synthetic tool for forming carbon-carbon bonds.
- Functionalized heteroaryl aldehydes present unique challenges in coupling reactions due to their electronic properties.
- Controlling diastereoselectivity in coupling reactions is crucial for synthesizing complex molecules.
Purpose of the Study:
- To develop a robust low-temperature Evans-Tishchenko coupling protocol for heteroaryl aldehydes.
- To investigate and optimize reaction conditions for high yield and diastereoselectivity.
- To identify and understand competing side reactions, such as the retro-aldol aldol-Tishchenko reaction.
Main Methods:
- Employing a Samarium(III) catalyst for the coupling reaction.
- Utilizing a range of functionalized heteroaryl aldehydes and β-hydroxy ketones as substrates.
- Performing reactions at low temperatures to favor the desired coupling pathway.
- Analyzing reaction mixtures to identify and quantify byproducts.
Main Results:
- Achieved high yields (90-99%) in the low-temperature Evans-Tishchenko coupling.
- Obtained good to excellent diastereoselectivity (90:10 to 95:5 dr).
- Identified a competing retro-aldol aldol-Tishchenko reaction at room temperature.
- Optimized conditions for the aldol-Tishchenko reaction for specific heteroaryl aldehydes.
Conclusions:
- The developed low-temperature protocol is effective for the Evans-Tishchenko coupling of heteroaryl aldehydes.
- Understanding byproduct formation allows for the optimization of related aldol-Tishchenko reactions.
- This work expands the scope and control of coupling reactions involving heteroaromatic systems.
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